Method for profiling bonding needles

ABSTRACT

In the bonding of a conductive wire to an electrical apparatus, the wire runs down through the hole in a hollow needle and extends at an angle of about 90* with the needle at the tip thereof and the wire as it exits from the needle is bonded to a bonding pad comprising part of an electrical apparatus by a combination of pressure and heat. If the inside and outside profiles of the tip of the hollow needle are not properly rounded, bad bonds will result in that the wire may break. A method and a means are disclosed for giving the tip of the needle a proper smooth and rounded profile both internally and externally.

United States Patent [54] METHOD FOR PROFILING BONDING NEEDLES 3 Claims,9 Drawing Figs.

[52] US. Cl 51/326 [51] Int. Cl B24b 1/00 [50] Field of Search 51/326Primary Examiner-Lester M. Swingle Att0rney-Mueller and AicheleABSTRACT: in the bonding of a conductive wire to an electricalapparatus, the wire runs down through the hole in a hollow needle andextends at an angle of about 90 with the needle at the tip thereof andthe wire as it exits from the needle is bonded to a bonding padcomprising part of an electrical apparatus by a combination of pressureand heat. If the inside and outside profiles of the tip of the hollowneedle are not properly rounded, bad bonds will result in that the wiremay break. A method and a means are disclosed for giving the tip of theneedle a proper smooth and rounded profile both internally andexternally.

' PATENTEUJAN 41912 3,631,645

j 34 H I 24 I I I I II INVENTOR. Harry da Costa 94 BY Char/es 6. Thom/onATTY'S METHOD FOR PROFILING BONDING NEEDLES BACKGROUND This inventionrelates to a method for giving the tip of a hollow needle used in wirebonding a proper profile.

In making connections to electrical apparatus such as that applied tochips, a bonding wire having a diameter of a little less than 00015 ofan inch may be used. This bonding wire is fed through a hollow needleand the portion thereof just outside the tip of the needle is bent overat about 90 to the needle. The needle is then pressed down onto a pointon the bonding pad of the electrical equipment to which the wire is tobe connected and the wire at the bend thereof is bonded to theelectrical apparatus by a combination of pressure and heat. The needleand the apparatus are moved with respect to each other to another pointwhere the wire is to be bonded and the bonding process is repeated. Wireis drawn down through the hollow needle during the process of moving theneedle and the apparatus with respect to each other. The needle is thendrawn a little further and the wire may be cut off or the wire may bebroken by rapid vibration or oscillation of the needle, leaving a longenough tail of wire extending from the tip of the needle so that anotherbond can be made. The shape of the tip of the needle is critical sincein the process of bonding due to the pressure applied thereto, a grooveor indentation or impression is made in the wire during the bondingwhereby the wire takes on the shape of the tip of the needle. If the tipof the needle is not properly smoothed and rounded, the wire bond may bedefective in that the wire may break at the indentation when force isapplied to the wire during the process of moving the needle with respectto the apparatus or during the process of intentionally cutting orbreaking the wire or during any other process, such as encapsulation,that may take place. The tip of the needle is tiny, it having an outsidediameter of about 0.004 of an inch and an inside diameter of about0.0015 of an inch. The profile of the tip at the inside of the needlecannot clearly be seen by the naked eye or by the aid of opticalinstruments. Therefore, the only way one could be sure that a new needlehad a proper tip profile was to try to make bonds with it and if thebonds made thereby were good then the needle had a proper tip profile.Furthermore, the only way that one could know that a needle was worn outwas when this needle began making bad bonds. Furthermore, repairing orrenewing the needle was a cut and try method whereby needles wereusually discarded when they began to make bad bonds. The cost ofdiscarded bad electrical apparatus produced by bad bonding needles andthe cost of replacement of bad bonding needles added substantially tothe cost of producing acceptable electrical apparatus.

It is the object of this invention to provide a method for preparing thetips of new bonding needles or for repairing the tips of worn ordefective bonding needles.

It is a further object of this invention to provide a method forobserving the profile of a surface which is itself difficult if notimpossible to observe directly.

SUMMARY In accordance with the invention, a hollow needle may beprepared for shaping by lapping the tip thereof to provide a tip that isperpendicular to the length of the needle. The tip of the needle isshaped by projecting particles of abrasive material towards the tip ofthe needle generally in directions parallel to or slightly divergentfrom the direction of the axis of the needle. Then the tip of the needleis polished by embedding the needle in an abrasive material and rotatingthe needle while so embedded. The profile of the inside and the outsideof the tip of the needle is observed by making an impression of the tipof the needle on a material such as the edge of a block or such as awire so that the shape of the needle through the center portion of thetip thereof or along the plane through the axis thereof may be observedby observing the impression made thereby.

DESCRIPTION The invention will be better understood upon reading thefollowing description in connection with the accompanying drawing inwhich FIGS. 1 and 2 are partial cross-sectional views of a needle takenat a plane through the axis thereof,

FIG. 3 is an elevational view of an abrasive blasting apparatus forshaping the tip of the needle of FIG. 1,

FIG. 4 is an elevational view of a polishing apparatus for polishing thetip of the needle of FIG. 1,

FIG. 5 is a cross-sectional view of the abrasive pad of FIG. 4 andshowing the relative position of the needle and the abrasive pad duringpolishing operation,

FIG. 6 is an elevational view of an apparatus for making an impressionof the profile of the tip of the needle preparatory to viewing it,

FIG. 7 is an illustration of the profile obtained by using the apparatusof FIG. 6,

FIG. 8 is a partial elevational view of a modification of the apparatusof FIG. 6, and

FIG. 9 is an illustration of the profile obtained by use of theapparatus of FIG. 8.

A known method of bonding a wire 10, see FIG. 2, to a bonding pad 11 isto run the wire 10 through the hollow 12 of a hollow needle 14 and bendthe wire 10 as it exits from the tip 18 of the needle 14 at a angle withthe length of the needle 14. The needle 14 is then pressed down on thebonding pad 11 and, by a combination of heat and pressure, the wire 10is bonded to the bonding pad 11. Due to this pressure, an impression 20is formed in the portion of the wire 10 that is under the tip 16 of theneedle 14. Then, the needle 14 and the bonding pad 11 are moved withrespect to each other until another bonding pad (not shown) is under theneedle 14 and needle 14 is pressed down on the other bonding pad,whereby a connection is provided between the two bonding pads. Then thewire 10 is cut or is broken by vibrating the needle 14 and anotherconnection may be made in a similar manner.

If the impression 20 in the wire 10 made by the needle 14 is not roundedand smoothed, that is, if the impression is jagged or angular, the wire10 may break away from its bonding pad 11 or it may break between thetwo bonding pads to which it is connected during further processing ofthe electrical apparatus, that is, if the tip profile of the needle 14is not smooth and rounded, the bonds made by the needle 14 may not bereliable.

The tip of the needle 14 has a diameter of about 0.004 of an inch andthe inside diameter of the hole through the needle is about 0.0015 of aninch. While it is possible to see the outside profile of the tip 18 withproper optical instruments, it is not possible to see the profile of theinside portion of the tip 18 in the vicinity of the hole 12 through theneedle 14. The needles 14 when bought new may therefore have a jagged orrough inside profile. Therefore, when new needles are bought they aretreated as if their inside profiles are bad. They and used needles thathave begun to produce bad bonds are treated alike.

New needles 14, see FIG. 1, as received, as well as used needles 14, arelapped in a known manner to produce a square tip 22. That is, afterlapping, the tip 22 comprises a plane which is perpendicular to thelength of the needle 14.

Then the needle 14 is put in a chuck 24 on a shaft 26 which is rotatedby a motor 28 at a few hundred revolutions per minute and an abrasivematerial such as aluminum oxide particles 30 having diameters of from 5to 30 microns is blown or projected directly at the tip of the needle 14as from a noule 32 which is about 3 inches from the tip of the needlefor from 5 to 60 seconds depending on the size of the abrasiveparticles. A housing 34 may be provided to prevent scattering of theabrasive particles.

After being exposed to the abrasive blast for the required length oftime, the needle 14 is taken out of the chuck 24 and put into a chuck 36which is rotated by a motor 38 at several thousand revolutions perminute. An abrasive pad 40 is provided which may be a straight grainedblock of wood impregnated with diamond dust, the grains of the wood pad40 being parallel to the axis of the needle 14. Then pad 40 is fixedlymounted on a shaft 44. The shaft 44 is slideably and rotatably mountedin the bearings 46 and 48. A plate 50 is fixed to the shaft 44 betweenthe bearings 46 and 48. A circular plate 52 is fixed to a shaft 54 whichextends perpendicularly to the shaft 44. The shaft 54 is rotated in abearing 56 at about r.p.m. by a motor not shown. The circular plate 52has a projection or lobe 58 projecting from the periphery of the plate52. The shaft 44 and the plate 50 as well as the pad 40 slide downwardwith respect to the bearings 44 and 46 due to gravity until the tip 18of the needle 14 is embedded in the stationary pad 40 as shown in FIG.5. The periphery of the plate 52 (except for the lobe 58) does notcontact the plate 50. Since the needle 14 is rotating at high speed andsince the tip 18 of the needle is embedded in the straight grained pad40, a portion of the pad 40 penetrates into the hollow 12 of the needle14 and both the outside and the inside profile of the tip 18 of theneedle 14 is polished by the pad 40. For each revolution of the shaft 54and the plate 52, the projection 58, by its contact with the plate 50,lifts the pad 40 off of the needle 14 and rotates the pad 40 a smallamount and then drops the pad 40, whereby the pad 40 presents newpolishing positions to the needle 14 at periodic intervals depending onthe speed of rotation of the shaft 54. After a few minutes in thepolishing machine illustrated in FIGS. 4-and 5, the treatment of the tip18 of the needle 14 is completed and the tip 18 is observed. As notedabove, due to the small size of the tip 18 of the needle 14, the insideof tip 18 cannot be observed directly. An apparatus for indirectlyobserving the needle tip 18 is shown in FIG. 6.

The needle 14 is held in a clamp 60 comprising two parts 62 and 64 whichare bolted together as by bolts and nuts 66. The needle 14 may be slidup and down on the rods 68 and 70 as by a handle 72 to cause contact ofthe tip 18 of the needle 14 with the junction of two soft blocks 74 and76. The blocks 74 and 76 are held in a vise 78 by turning a thumb nut 80and the junction of the blocks 74 and 76 can be moved to be in exactline with the axis of the needle 14 by turning the screw 84 by means ofa thumb nut 82, which causes lateral motion of the vise 78. An opticalinstrument (not shown) may be used to help align thejunction of theblocks 74 and 76 with the needle 14. When the needle 14 is pressed down,an annular groove or impression (not shown) is formed, one-half in eachof the two blocks 74 and 76. Then, when the blocks 74 and 76 are removedfrom the clamp 78, the edge of the grooves 90 and 92 (see FIG. 7), maybe examined by the eye, with the aid of an optical instrument ifdesired, to make sure that the grooves 90 and 92, and therefore theshape of the tip of the needle 14, are smoothly rounded off. If itappears necessary, the needle 14 may be turned 90 about its axis andanother impression of the tip 18 thereof may be taken.

If desired, a wire 94 may be laid on the top of a block 96 in a groove98 therein. The wire 94 may be fixed to a pin 100 which projects fromthe front of the block 96. The wire 94 may be lined up with the needle14 (not shown in FIG. 8) by turning the screw 84 by means of the thumbnut 82. The diameter of the wire 94 is about equal to the diameter ofthe hole 12 in the needle 14. When the alignment of the needle 14 andthe wire 94 is complete, the axis of the needle 14 and the axis of thewire 94 intersect, these axes being at right angle to each other. Whenthe impression of the tip 18 of the needle is made into wire 94 as bythe means shown in FIG. 6, the grooves or impressions in the top of thewire 94, see FIG. 9, may be examined for smoothness of curvature by anysuitable optical means. If the smoothness and curvature are notsuitable, the needle 14 may be reprocessed as noted above.

A method and an apparatus for shaping the outside and the insidecurvature of the tip of a hollow needle which is so small in insidediameter that the inside diameter cannot be checked by known opticalmeans has been disclosed.

We claim: I j 1. A method of shaping the tip of a hollow needle havingan axis extending through the bottom thereof and a tip surrounding saidaxis which comprises lapping the tip of the needle to give it the shapeof a plane perpendicular to the axis of the needle,

abrading the tip of the needle with particles of abrasive material thatare projected generally along the axis of the needle and into said tip,

polishing said tip by rotating said needle while embedded in a straightgrained pad which is impregnated with polishing materials, said grainextending parallelly to the axis of said needle, and

checking the shape of the tip of said needle by forming an impressionthereof in an impressionable material and observing the shape of saidimpression at a position corresponding to a central portion ofsaidneedle.

2. The invention of claim 1 in which said impression is formed bypressing the tip of said needle on two blocks at the junction thereof,the axis of said needle extending through the junction of said twoblocks.

3. The invention of claim 1 in which said impression is formed bypressing the tip of said needle into a wire, the axis of said needle andof said wire intersecting and extending perpendicular to each other.

1. A method of shaping the tip of a hollow needle having an axisextending through the bottom thereof and a tip surrounding said axiswhich comprises lapping the tip of the needle to give it the shape of aplane perpendicular to the axis of the needle, abrading the tip of theneedle with particles of abrasive material that are projected generallyalong the axis of the needle and into said tip, polishing said tip byrotating said needle while embedded in a straight grained pad which isimpregnated with polishing materials, said grain extending parallelly tothe axis of said needle, and checking the shape of the tip of saidneedle by forming an impression thereof in an impressionable materialand observing the shape of said impression at a position correspondingto a central portion of said needle.
 2. The invention of claim 1 inwhich said impression is formed by pressing the tip of said needle ontwo blocks at the junction thereof, the axis of said needle extendingthrough the junction of said two blocks.
 3. The invention of claim 1 inwhich said impression is formed by pressing the tip of said needle intoa wire, the axis of said needle and of said wire intersecting andextending perpendicular to each other.